<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>Title</title>
</head>
<body>
<div id="app">
  <h2>{{counter}}</h2>
  <button @click="increament">+</button>
  <button @click="decreament">-</button>
</div>

<script src="./js/vue.js"></script>

<script>
  const app = new Vue({
    el:'#app',
    data:{
      message:'Hello World',
      counter:0
    },
    methods:{
      increament(){
        this.counter++;
      },
      decreament(){
        this.counter--;
      }
    }
  });
</script>
</body>
</html>